1. Field of the Invention
The present invention generally relates to vehicle suspension systems. More particularly, the present invention relates to interrelated multiwheel suspension systems that provide improved damping when a vehicle rolls or pitches and a single wheel encounters a bump.
2. Description of Related Art
Vehicles often comprise suspension systems that smooth operation over uneven or rough terrain. The suspension systems often involve placing a damper between the vehicle and the surface contacting member, such as a wheel. An example of a suspension system used in four-wheel vehicles has been disclosed in Japanese laid open patent application No. HEI-6-62127. Reproduced as FIGS. 1–3 in the present application are figures that disclose a construction similar to that disclosed in that laid open application.
With reference now to FIGS. 1–3, three alternative constructions of a suspension system will be described. The suspension system, indicated generally by the reference numeral 20, comprises a front left damper 22, a front right damper 24, a rear left damper 26, and a rear right damper 28. In the illustrated arrangement, each of the dampers is constructed identical to the others. In particular, in the illustrated arrangement, an outer cylinder 30 is divided into an upper chamber 32 and a lower chamber 34 by a piston 36. The piston 36 is slidably mounted within the inner bore of the outer cylinder 30. In addition, the piston comprises at least one passage 38 which extends through the body of the piston 36 to place the upper chamber 32 and the lower chamber 34 in fluid communication with each other. A throttle 40 preferably is disposed within the passage 38 to control the flow rate through the passage 38 of fluid from the upper chamber 32 to the lower chamber 34, and vice versa. Of course, more than one passage can be used and such passages can be configured with valves that limit flow to one direction. Such a configuration allows varying damping rates between the two different directions of piston movement. In the illustrated arrangement, the piston 36 is mounted to a piston rod 42. One of the piston rods 42 and the cylinder 30 is connected to the vehicle body while the other of the two members is connected to the wheel. In this manner, movement between the wheel and the vehicle body can be controllably damped by movement of the piston 36 within the bore of the outer cylinder 30.
With continued reference to FIGS. 1–3, each of the cylinders 22, 24, 26, 28 is directly interconnected through the use of a pressure regulator 44. FIGS. 1–3 illustrate four different arrangements of the pressure regulator 44 and the interconnection between the cylinders 22, 24, 26, 28. Depending upon the interconnection used, the suspension systems 20 exhibit varying response characteristics to movement of the vehicle.
With reference now to FIG. 1, the illustrated pressure regulator 44 generally comprises a pair of parallel lower chambers 46, 48. The first lower chamber 46 is defined within a first cylinder 50, while the second lower chamber 48 is defined within a second cylinder 52. A first piston 54 subdivides a portion of the first cylinder 50 into the first lower chamber 46 while a second piston 56 subdivides a portion of the chamber or the cylinder 52 into the second lower chamber 48. The pistons 54, 56 are connected together with the use of a single connecting rod 58 that ties the pistons 54, 56 together for movement. In other words, the connecting rod 58 ensures that the pistons 54, 56 travel together. In the illustrated arrangement, the connecting rod 58 is disposed within a chamber 60 that is defined within the pressure regulator 44. The chamber 60 preferably is filled with an inert gas. The inert gas exerts a pressure against the pistons 54, 56 to drive the pistons into a desired equilibrium position. A passage 62 containing a throttle valve extends between the first lower chamber and the second lower chamber 48. The passage 62 contains the throttle to allow damping to occur when fluid flows from one chamber to the other chamber.
The pressure regulator illustrated in FIG. 2 has a construction similar to that illustrated in FIG. 1. However, the pressure regulator 44 illustrated in FIG. 3 contains two additional chambers 64, 66 that are interconnected in parallel by two additional throttled passages 68, 70. The chambers 64, 66 are also defined, in part, by a pair of pistons 72, 74 that are interconnected with the connecting rod 68.
Functionally, the suspension systems 20 illustrated in FIGS. 1–3. operate differently depending upon the loads and relative movements of the vehicle. For instance, in the arrangement illustrated in FIG. 1, both of the dampers 22, 26 on the left side of the vehicle are interconnected to a single chamber of the pressure regulator 44 while both of the dampers 24, 28 on the right side of the vehicle are connected to a second chamber of the pressure regulator 44. Such a construction results in flow through the throttled passage 62 that extends between the chambers 46, 48 when the vehicle rolls or otherwise sways laterally. Such flow results from the differing movements of the dampers on the left side of the vehicle and the dampers on the right side of the vehicle. As working oil flows through the throttle passage 62, the movement of the pistons is further damped by the restriction of the throttled passage. The arrangement illustrated in FIG. 1, however, results in little flow between the two chambers through the throttle passage 62 when the vehicle pitches, such as during rapid acceleration or deceleration.
With reference now to the arrangement illustrated in FIG. 2, the dampers 22, 28 and the dampers 24, 26 are interrelated and are connected to the chambers 46, 48, respectively. In other words, the vehicle supported by the suspension system 20 illustrated in FIG. 2 features cross-related dampers (i.e., left front damper 22 and right rear damper 28 are connected to a single chamber while the right front damper 24 and the left rear damper 26 are connected to a second chamber). This cross-arrangement results in increased damping forces caused by flow through the throttle passage 62 when the vehicle is twisted such as occurs when accelerating or decelerating into a corner or out of a corner. In other words, when the pressure is increased at one corner of the vehicle relative to the other three corners, increased damping results from flow between one of the chambers 46, 48 into the other of the chambers 46, 48 of the pressure regulator 44.
With reference now to FIG. 3, each of the dampers 22, 24, 26, 28 is connected to its own chamber 46, 64, 66, 48, respectively. The adjacent chambers such as 46, 64, or 64, 66 or 66, 48 are directly interconnected by throttle passages. In this manner, when the vehicle rolls (i.e., rotates about a longitudinally extending axis) differential pressures result within the two chambers associated with the left side of the vehicle as compared to the two chambers associated with the right side of the vehicle. Accordingly, working oil flows through three throttle passages (68, 70, 62) to equalize the differentials in the oil pressure. Thus, the pressure regulator 44 provides increased damping force during rolling movement of the vehicle body. In addition, with the suspension system 20 illustrated in FIG. 3, when the vehicle body pitches (i.e., rotates about a transversely extending axis) working oil passes between the chambers 46, 64 and 66, 48 through the throttle passages 68 and 62. This results in the pressure regulator 44 increasing the available damping forces during pitching of the vehicle.
It has been found, however, that each of the above-described arrangements suffers from a similar problem. In particular, when the paired dampers move in the same direction and one of the wheels associated with one of the dampers suddenly negotiates a bump in the road, the desired damping forces that resist rolling and pitching can be reduced. For example, in the arrangement illustrated in FIG. 1, if the dampers 22 and 26 are extending, whereby the volume of the lower chambers 34 is increasing, while the dampers 24, 28 are contracting, whereby the volume in the lower chambers 34 is decreasing, such that the working oil is flowing from right to left through the throttled passage 62, the flow rate through the throttle passage 62 will undesirably decrease should one of the dampers 22, 26 suddenly contract or should one of the dampers 24, 28 suddenly extend. The sudden extension or contraction, such as that encountered during operation over a bump or through a rut, therefore, will rapidly decrease the damping force available for restricting rolling. A similar result would arise in the arrangements illustrated in FIGS. 2 and 3 as well.
Accordingly, a suspension system is desired in which the damping force during pitching or rolling of the vehicle body is substantially uneffected by irregularities in the road surface.